Thiram

Phototransformation in water

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

key study

Study period:

22 September 1989 -16 July 1990

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Study type:

direct photolysis

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-2 (Photodegradation Studies in Water)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Analytical method:

gas chromatography

high-performance liquid chromatography

other: TLC

Details on sampling:

Samples were taken after the exposure time of 2, 4, 7, 10, 12, 18, and 30 hours (phase I).
For the quantitative extraction of the volatiles, three vessels were exposed to sunlight for 2, 4, or 6 hours (phase II).

- Sampling intervals for the parent/transformation products: After 2, 4, 7, 10, 12, 18, and 30
Hours exposure (the last two samples were in the photolysis unit for 30 hr and 54 hr, respectively). Because the light source was natural sunlight (an intermittent light source), the samples were exposed to 12 hours of light every 24 hours that they were in the photolysis unit; therefore, a sample in the photolysis unit for 30 hours would have been exposed to light for 18 hours.
- Sampling method: At each sampling time, duplicate samples were removed from the photolysis unit for analysis.
- Sampling methods for the volatile compounds, if any: The first set of samples was immediately placed on a purge-trap system. The purge-trap system was comprised of an activated carbon trap (8 g activated carbon) and a sodium hydroxide trap (50 mL of 1 M NaOH). The samples were purged for 15 minutes. The trapped volatiles were removed from the activated carbon by soaking the carbon in 50 mL of methanol. The methanol solution was then radioassayed. The remaining activated carbon was analyzed by oxidative combustion in a Harvey Biological Materials Oxidizer, followed by radioassay. The sodium hydroxide solution was radioassayed directly.

Buffers:

pH 5 Acetate buffer

Light source:

sunlight

Details on light source:

- Location: Colorado Springs, Colorado, USA
- Latitude: 39° N
- Longitude: 104° W
- Light intensity: 1.1x10exp-6 to 9.9x10exp-7

Details on test conditions:

TEST SYSTEM
- Each test vessel was a thin-walled quartz test tube (9/16“ x 4“). The test tube was sealed with a sheet of Teflon (0.005'') and capped vith a Teflon cap. The Teflon cap was sealed with silicone rubber to insure volatiles were not lost. Prior to use, all glassware was sterilized in a pressure cooker (121 °C for 30 minutes) to minimize biodegradation.

TEST MEDIUM
- A 1 mg/mL stock solution of 14C-thiram was prepared in chloroform, and 200 uL were added to each test tube. The chloroform was removed under a stream of nitrogen, then 20 mL of the pH 5 acetate buffer was added to each test tube, to achieve a nominal 14C-thiram concentration of 10 ppm.
The water solubility of thiram is reported to be 16.6 ppm2. The samples were sonicated for 5 minutes to redissolve the 14C-thiram. Each tube was then capped as previously described and placed in the photolysis apparatus.

REPLICATION
- No. of replicates (dark): 2
- No. of replicates (irradiated): 2

Duration:

54 h

Temp.:

25 °C

Initial conc. measured:

8.9 mg/L

Reference substance:

yes

Dark controls:

yes

DT50:

8.8 h

Test condition:

25°C

Predicted environmental photolytic half-life:

8.8 hours

Transformation products:

yes

¹⁴C-THIRAM photolysis half-life calculation

Time point (hours)	THIRAM		Predicted
	ppm	ln ppm	ln ppm
0	8.93	2.189	2.068
2	6.32	1.844	1.911
4	5.00	1.609	1.754
7	4.87	1.583	1.519
10	3.71	1.311	1.284
Photodegradation rate constant	0.07833 1/h
Photodegradation half-life	8.8 hours

Distribution of radioactivity in photolysis solutions after treatment with ¹⁴C-THIRAM (results given in percent of RA)

Time point (hours)	Chloroform extract	Remaining in aqueous solution	Volatiles*	Total recovery after analysis (rounded values)
2	79.32	1.87	11.3	92.5
4	65.50	4.89	14.6	85.0
7	65.04	4.18	23.3	92.5
10	53.20	9.07	29.2	91.5

* = volatiles as determined from the loss of activity during purging.

Validity criteria fulfilled:

yes

Conclusions:

A short photolysis half-life of 8.8 hours indicates that the 14C-THIRAM breaks down rapidly in water, when exposed to natural sunlight.
The major breakdown product was volatile CS2. Other breakdown products were also isolated, although they represented less than 10 % of the initial radioactivity at the study termination. Due to their instability in solution, the identification of them was difficult. The unstable degrades were most likely dimethyldithiocarbamic acid (DMDTC) and dimethylaminothioxomethanesulfenic acid (DMATMS).
Due to presented results, it should be underlined that photolysis will significantly contribute to the overall degradation of THIRAM in aquatic systems.

Executive summary:

Materials and methods: This study was performed according to EPA FIFRA, part 161-2: Photodegradation in Water and initiated to determine the aqueous photodegradation rate constant and half-life of 14C-THIRAM under natural sunlight conditions. This study consisted of two phases. The first phase was performed to determine the kinetics for the breakdown of test item and formation of its photolysis products. The second phase was conducted particularly to produce enough degradation products for identification by mass spectrometry (MS). Both phases were run at 8.9 ppm in pH 5 buffer.

Results and discussion: The photolysis of THIRAM was studied in pH 5 acetate buffer at a concentration of 8.9 ppm 14C-THIRAM. The buffered 14C-THIRAM solution was exposed to natural sunlight. Under these conditions, 14C-THIRAM rapidly broke down.
The major breakdown product was volatile CS2, which was continuously formed during the study. Other degrades (HPLC-peaks 3, 4, 5) were isolated in the chloroform extract. At the half-life time point (8.8 hours) these peaks presented less than 7.5% of the initial radioactivity, whereas THIRAM and CS2 were the major components.
Only one degradation product (the peak 5) in the chloroform extract increased over the time of experiment and achieved 6.25% of the initial radioactivity after 12 hours of exposure.
The remaining aqueous phase after chloroform extraction contained less than 10% of the initial radioactivity after 12 hours of exposure. This radioactivity was comprised of three breakdown products.
The MS analysis indicated that the photoproducts isolated by HPLC from the chloroform extract were unstable and were converted to the more stable dimethyldithiocarbamic acid methyl ester during the isolation and analysis procedures. The unstable degrades were most likely dimethyldithiocarbamic acid (DMDTC) and dimethylaminothioxomethanesulfenic acid (DMATMS).

Reference 2

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

key study

Study period:

06 January 1994 - 02 March 1994

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Study type:

direct photolysis

Qualifier:

according to guideline

Guideline:

other: OECD Draft Test Guideline: “Phototransformation of Chemicals in Water” prepared by Umweltbundesamt Berlin

Version / remarks:

1990

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Ministry of Environment, Energy and Federal Affairs, Germany

Radiolabelling:

yes

Analytical method:

high-performance liquid chromatography

other: TLC... (see attached file)

Details on sampling:

After 0.25, 0.5, 1.0, 4.0 and 24 hours of irradiation one sample of test solution per sequence was withdrawn and measured by LSC in duplicate (1.0 mL of each sample).
One sample was analysed without irradiation at time 0.
Additionally two actinometer solutions were irradiated at the beginning and at the end of each set of samples irradiated and compared with a non irradiated actinometer solution.

Buffers:

Phosphate buffer at pH 7

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

290

Details on light source:

1.8 kW Xenon burner and 290 nm UV-filter

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test apparatus/vessels: The samples were incubated in irradiation cuvettes (glass with quartz cover).
- The dark control was incubated in a tightly closed boro silicate LSC vial.
From the test solution seven subsamples of 20 mL per sample sequence were taken and transferred to the irradiation cuvettes (glass with quartz cover).
In addition one 20 mL subsample per sample sequence was incubated at 20°C ± 2°C for 24 hours in the dark to obtain stability data of 14C-THIRAM in non sterile test system.
For determination of the number of photons penetrating the test solution cells an uranyl nitrate/oxalic acid actinometer was used.
- The irradiation was performed in duplicate. For each sample sequence the test solution was freshly prepared.

Duration:

24 h

Temp.:

20 °C

Initial conc. measured:

10.25 mg/L

Reference substance:

yes

Remarks:

Thiram

Dark controls:

yes

Computational methods:

Calculation of quantum yield was performed with a programme named QUANTAUS vers. 1.10. The calculations base on results of HPLC characterisation of radioactivity.

Preliminary study:

Not performed

Quantum yield (for direct photolysis):

0.003

DT50:

4.1 h

Test condition:

20°C

Predicted environmental photolytic half-life:

4.1 hours

Transformation products:

not measured

Concentration of ¹⁴C-THIRAM in test solution determined by TLC and HPLC (results given in mg/l)

Identification	Irradiation Times [hours]
	0		0.25		0.5		1.0		2.0		4.0		24.0
	TLC	HPLC	TLC	HPLC	TLC	HPLC	TLC	HPLC	TLC	HPLC	TLC	HPLC	TLC	HPLC
1^st sample sequence	9.8	10.3	9.7	10.0	9.7	9.9	9.4	9.2	7.4	7.0	5.6	5.4	n.d.	n.d.
2^nd sample sequence	8.8	10.1	9.0	9.9	8.9	9.6	8.4	8.9	6.2	6.9	4.5	5.3	n.d.	n.d.
Mean value	9.3	10.2	9.4	10.0	9.3	9.8	8.9	9.1	6.8	7.0	5.1	5.4	n.d.	n.d.
Stability in test system (not irradiated sample)	9.3	10.2	n.p.	n.p.	n.p.	n.p.	n.p.	n.p.	n.p.	n.p.	n.p.	n.p.	7.7	10.0

n.p. = not performed
n.d. = not detectable (value below 0.05 mg/l)

Applied radioactivity (AR) of ¹⁴C-THIRAM detected in test solution (expressed as % of AR)

Identification	Irradiation Times [hours]
	0	0.25	0.5	1.0	2.0	4.0	24.0
1^st sample sequence	100.21	100.30	99.78	98.92	97.98	92.82	35.84
2^nd sample sequence	99.12	99.54	99.82	100.07	97.93	91.52	41.51
Mean value	99.67	99.92	99.80	99.50	97.96	92.17	38.68
Stability in test system (not irradiated sample)	99.67	n.p.	n.p.	n.p.	n.p.	n.p.	98.71

n.p. = not performed

Validity criteria fulfilled:

yes

Conclusions:

A short aqueous photolysis half-life of 4.1 hours was determined for the active substance THIRAM. Photolysis will significantly contribute to the overall degradation of THIRAM in aquatic systems.

Executive summary:

Materials and methods: The test was performed according to OECD Draft-Test Guideline: “Phototransformation of chemicals in water” prepared by Umweltbundesamt Berlin, January 1990.

Results and discussion: THIRAM concentration rapidly decreased from an initial value of 10.25 mg/L to 0.05 mg/L (detection limit of HPLC) after 24 hours. The aqueous photolysis half-life was calculated to be 4.1 hours.

The quantum yield of direct photolysis of 14C-THIRAM in a buffered medium at pH 7 was determined in a laboratory study using Suntest irradiation apparatus and the computer programme Quantaus. The stability of 14C-THIRAM in dark test system at pH 7 was proved for maximum irradiation time period. The results indicate, that 14C-THIRAM showed a good stability without irradiation for at least 24 hours. Only 2 % of the applied radioactivity was lost.

Reference 3

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Study type:

not specified

Qualifier:

no guideline followed

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Light source:

other: solar and ultraviolet radiation

Reference substance:

not specified

Dark controls:

not specified

Transformation products:

yes

The results of this study validate the findings reported in other THIRAM hydrolysis and photolysis studies. The major degradation product is volatile carbon disulfide. Trace minor products, DMDTC and DMMMS, identified as transient products in solution in the previous studies were derivatized to form the more stable methyl DMDTC in this current study.

Validity criteria fulfilled:

not applicable

Description of key information

Tetramethylthiuram disulfide (CAS No. 137-26-8) photodegrades rapidly in water (DT50 = 8.8 hours, natural sunlight, EPA 161-2).

Key value for chemical safety assessment

Half-life in water:

8.8 h

Additional information

The photolytic degradation in water of tetramethylthiuram disulfide (CAS No. 137-26-8) was investigated in two studies (1990 and 1994). The first test (1990) was carried out according to EPA’s Pesticide Assessment Guidelines, Series 161-2, Photodegradation Studies in Water (1988), under GLP conditions. A 14C-thiram solution (pH 5 and test concentration = 8.9 mg/L) was exposed to natural sunlight at 25°C. The results showed a rapid photodegradation of the test compound, with a half-life of 8.8 hours. CS2 was the major degradation product. The second (1994) study was conducted according to OECD Guideline draft: Phototransformation of Chemicals in Water – Direct and Indirect Photolysis, under GLP conditions. A 14C-thiram solution (pH 7 and test concentration = 10.25 mg/L) was exposed to artificial light (xenon lamp) at 25°C. Radioactivity was quantified by LSC and characterised by TLC and HPLC. The resulting predicted half-life was 4.1 hours. A third supporting study is available (1990), which investigated the identity of metabolites formed due to photolysis. The major degradation product was found to be volatile carbon disulfide. Trace minor photolysis products were identified by MS and NMR as methyl dimethyldithiocarbamate (methyl-DMDTC), which was the more stable form of the thiram metabolites dimethyldithiocarbamate (DMDTC) and dimethylaminothioxo-ethanesulfenic acid (DMATMS).

 

In view of these results, it can be concluded that photolysis will significantly contribute to the overall degradation of tetramethylthiuram disulfide in aquatic systems.